The present invention relates to a golf club head, more particularly to a structure of the clubface.
In general, a wood-type golf club head has a clubface provided with a bulge (a curvature from heel to toe) and a roll (a curvature from crown to sole).
Such clubface roll has a function to decrease the difference in the backspin of the hit ball between the on-center shot (at the sweet spot) and vertically off-center shots (on the upside or downside of the sweet spot) as well-known in the art. If there is no roll namely the clubface is flat, then due to the so called vertical gear effect, the backspin is decreased in the case of upper shots, but in the case of lower shots, the backspin is increased. Thus, depending on the ball hitting position, the backspin varies widely. By providing a clubface roll, however, the gear effect is lessened and the variation of the backspin is reduced although the backspin in the on-center shot is still more than that in the upper shot and less than that in the lower shot due to the gear effect.
Further, in the case of the upper shot, the clubface roll can increase the launch angle of the hit ball, and thus compensate a decrease in the ballistic height due to the decrease in the backspin from that in the on-center shot.
In the case of the lower shot, on the other hand, the clubface roll can decrease the launch angle of the ball, and compensate an increase in the ballistic height due to the increase in the backspin from that in the on-center shot.
Thus, the difference in the backspin between the on-center shot and vertically off-center shots can be reduced.
On the other hand, the clubface is provided with grooves in a pattern so called score lines. If there is no groove, the frictional force between the clubface and the ball at impact is reduced, and the backspin is lessened. As a result, it becomes difficult to obtain the necessary backspin in a wet condition and the hit ball drops early from the sky, largely loosing the carry distance. By providing the grooves, the friction between the clubface and ball is increased, and the lack of backspin in the wet conditions can be prevented and the loss of the carry distance is decreased. But, in the dry conditions, due to the increased friction between the clubface and ball, the above-mentioned vertical gear effect has a tendency to increase, and as a result, the difference in the backspin between the on-center shot and vertically off-center shots has a tendency to increase again although the clubface roll is provided.